This invention relates to connector-cable assemblies such as used to make multiple interconnections between high speed circuits in computers, and similar electronic equipments.
Many present day electronic circuits (semi-conductors, large scale integrated circuits, etc.) have much higher densities, and faster switching speeds, than circuits of only five years ago. These modern circuits produce signal pulses with nanosecond, or even sub-nanosecond rise times, and relatively low power. Where it is necessary to transmit with high integrity the signals from one circuit to another that is physically removed by some distance (e.g. five feet), present day practice frequently is to use a flat cable with multiple signal lines. Each line of the cable has an impedance that is closely matched to the impedance of the circuits it is interconnecting. This impedance matching is necessary to prevent undue amounts of distortion, of attenuation, and of cross-talk of low power electronic signals traveling along the lines in the cable. Cables with impedance in the range from 50 to 95 ohms, and with from eight to forty signal lines are commonly used.
For reasons of mechanical, thermal and electronic performance, and also because of efficient size and installed cost advantage, a widely used type of matched impedance cable comprises a thin, flat ribbon of tough, low loss insulation, such as Teflon (Du Pont trademark). Buried in the insulation, are many fine gage, closely spaced wires which serve as multiple transmission lines. The wires are usually arranged in triplets in which a center signal wire is closely paralleled on each side by a ground wire. The impedance of each "triplet" transmission line is determined by the effective dielectric constant of the insulation surrounding them, by the gage of the wires, and by their distances apart.
By way of example, and as an aid in understanding the invention described hereinafer, one such flat cable which is typically used, comprises a thin ribbon of PTFE Teflon in which are buried sixty-six plated copper wires of 32 gage each. The wires are arranged in twenty-two "triplets" with a normal 50 mil (50 thousandths of an inch) center-to-center spacing from signal wire to signal wire. The cable insulation is about 30 mils thick and 1.13 inch wide. The impedance of each triplet line is nominally 95 ohms (plus or minus a few percentage points because of manufacturing tolerances). This impedance is measured with sub-nanosecond rise time pulses, which showed a propagation delay of slightly under 1.4 nanosecond per foor along ten feet of the cable.
In the inventor's previous pats. U.S. Pat. Nos. 4,173, 388 and 4,288,917 there are described a contact device for, and a method of, mechanically terminating the fine gage wires of a flat cable. The cable shown in these prior patents comprised twenty-four fine wires uniformly spaced on 31.5 mil centers (1/32 of an inch), giving somewhat over 90 mils for the center-to-center spacing of the signal wires. The output sockets were in a single row and spaced on 125 mil (1/8 inch) centers. The left-most and right-most sockets (sockets no. 1 and no. 10 in FIG. 6 of U.S. Pat. No. 4, 173,388) were the only ones connected to "ground"; the center eight sockets (nos. 2-9) were connected to "signals". The wire contacts were designed with a wide open end or "throat" (for reasons explained in the patent). They were made thick enough so that where a wire was crimped in the "neck " of a contact, the bottom of the wire did not protrude beneath the bottom of the contact. The contacts for the signal wires could be made relatively wide because of the relatively wide spacing of the signal wires (about 90 mils).
Very high reliability of the wire terminations made according to these prior patents was obtained. But various additional design considerations led to manufacturing and assembly complexities in changing to a different cable-connector combination in which there were many more wires, or wires on much closer centers, or with a different "ground" and "signal" pattern for the output sockets.
A less than optimum solution to some of these problems is shown in the inventor's U.S. pat. No. 4,225,208. Here the signal wires and the ground wires were spaced about half as far apart (here, nominally about 17 mils center-to-center). Partly because of this closer spacing, partly because of the need to mix the sequence of output ground and signal sockets and to provide two rows of them, and partly for other reasons, it was necessary to "spread" or manipulate certain of the ground and signal wires from the spacings they originally had in the cable. This is clearly shown in FIG. 4 of the patent. Such an arrangement was complex and expensive, and involved a considerable amount of "hand" labor.
The present invention is intended to obviate many of these prior difficulties, and to give a connector-contact system having greater reliability and substantially lower cost. The present invention is highly useful in, but not limited to, the connector system shown in the inventor's copending application filed on even date herewith, titled IMPROVED FLAT CABLE-CONNECTOR ASSEMBLY.
It is an object of this invention to provide an improved contact device and method for mechanically terminating fine gage, closely spaced wires.
It is a further object to provide an electronic flat cable connector having improved performance, reliability and manufacturability.
Still another object of the invention is to provide simple, inexpensive and highly reliable applicator tooling and a method for connecting the cable wires to the connector.